powerpc/86xx: Add MSI section to GE PPC9A DTS

Add the MSI section to the DTS file for the GE PPC9A.

Signed-off-by: Malcolm Crossley <malcolm.crossley2@gefanuc.com>
Signed-off-by: Martyn Welch <martyn.welch@gefanuc.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>